Underdetection of COVID-19 cases in France in the exit phase following lockdown

Abstract

A novel testing policy was implemented in May in France to systematically screen potential COVID-19 infections and suppress local outbreaks while lifting lockdown restrictions. 20,736 virologically-confirmed cases were reported in mainland France from May 13, 2020 (week 20, end of lockdown) to June 28 (week 26). Accounting for missing data and the delay from symptom onset to confirmation test, this corresponds to 7,258 [95% CI 7,160-7,336] cases with symptom onset during this period, a likely underestimation of the real number. Using age-stratified transmission models parameterized to behavioral data and calibrated to regional hospital admissions, we estimated that 69,115 [58,072-77,449] COVID-19 symptomatic cases occurred, suggesting that 9 out of 10 cases with symptoms were not ascertained. Median detection rate increased from 7% [6-9]% to 31% [28-35]% over time, with regional estimates varying from 11% (Grand Est) to 78% (Normandy) by the end of June. Healthcare-seeking behavior in COVID-19 suspect cases remained low (31%) throughout the period. Model projections for the incidence of symptomatic cases (4.5 [3.9-5.0] per 100,000) were compatible with estimates integrating participatory and virological surveillance data, assuming all suspect cases consulted. Encouraging healthcare-seeking behavior and awareness in suspect cases is critical to improve detection. Substantially more aggressive and efficient testing with easier access is required to act as a pandemic-fighting tool. These elements should be considered in light of the currently observed resurgence of cases in France and other European countries.

Diagnostic performance and clinical implications of rapid SARS-CoV-2 antigen testing in Mexico using real-world nationwide COVID-19 registry data

“…In order to address these methodological issues, the World Health Organization (WHO) proposed that rapid antigen tests (Rapid Ag-T) and other point-of-care tests (POCTs), which have demonstrated to have a high specificity compared to other molecular techniques 4,5 , could be useful alternatives for large-scale epidemiologic monitoring. With the worldwide rise in the use of Rapid Ag-T and POCTs, the presence of false negative results becomes of high epidemiologic importance, as unknown infected persons can be a vector of community transmission in countries where active SARS-CoV-2 infection is ongoing 8 .…”

A Framework for Assessing Social- and Location-Based Transmission Risk as a Heuristic for Individual Decision-Making

“…A comprehensive Spanish serology study indicated that one out of every 10 individuals with COVID-19, was correctly identified through testing [13]. This result was replicated in France as well [19]. Therefore, we must correct our disease prevalence data with a parameter, a ∈ (0, 1] which reflects the ascertainment rate, the ratio of recorded cases to actual cases.…”

Group testing as a strategy for COVID-19 epidemiological monitoring and community surveillance

“…Regarding symptomatic individuals, we assume the distribution of testing time to be modelled as a Gamma distribution G ( t ) = Γ α , β ( t ) with parameters α = 2 and β = 3 day −1 , see Fig 3 ; for simplicity, we consider such distribution to be independent of the epidemic status, although a realistic model could include an additional time delay in getting a test during high incidence phases, [ 60 ]. Based on both models Eqs 9 and 8 , we observe the relatively equally distributed viral load, see Fig 3F ; such distribution is in qualitative agreement with the behaviour observed in Fig 2E .…”